Chucks for supporting solar cell in hot spot testing

ABSTRACT

In an embodiment, a chuck to support a solar cell in hot spot testing is provided. This embodiment of the chuck comprises a base portion and a support portion disposed above the base portion. The support portion is configured to support the solar cell above the base portion and to define a cavity between a bottom surface of the solar cell and the base portion that thermally separates a portion of the bottom surface of the solar cell from the base portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/703,378, filed Feb. 10, 2010, the entire contents of which are herebyincorporated by reference herein.

FIELD

The present disclosure relates generally to semiconductor testingapparatuses. In an embodiment, the disclosure relates to chucks forsupporting a solar cell in hot spot testing.

BACKGROUND

Localized heating, or “hot spots,” in a solar cell can occur because ofinterconnection failure, cell failure, partial shading, mismatch ofphoto current from solar cell to solar cell, and/or partial shading. Forexample, when a single solar cell connected in series generates lesscurrent than other solar cells in the series, localized heating mayoccur because the current flowing through each solar cell in the seriesis not equal. Damage to, for example, a module of solar cells can occurif the localized heating of one or more solar cells become too high.

Many tests have been developed to test the ability of a solar cell towithstand hot spot heating. In these tests, a solar cell can reach atemperature of approximately 120° C., and this heat is not easilydissipated during testing. When testing a large number of solar cells,the tests need to be stopped or delayed for a certain time between eachsolar cell to allow a testing apparatus to cool down. However, thisdelay reduces the speed of the tests and therefore allows only a verylimited number of solar cells to be tested at a given time.

SUMMARY

In an embodiment, a chuck to support a solar cell in hot spot testing isprovided. Here, the solar cell has a top surface and a bottom surface.This chuck comprises a base portion and a support portion disposed abovethe base portion. The support portion is configured to support the solarcell above the base portion and to define a space, between the bottomsurface of the solar cell and the base portion, that thermally separatesa portion of the bottom surface of the solar cell from the base portion.It should be noted that, in this embodiment, the portion of the bottomsurface that is thermally separated comprises between about 70% andabout 90% of the bottom surface, which has metal conductors. However,the top surface is absent of any metal conductors. The chuckadditionally comprises a bore through the base portion and the supportportion. This bore is configured to allow a probe to make contact withthe metal conductors through the bore. The probe is configured to applya negative bias voltage to the solar cell.

In another embodiment, a hot spot testing apparatus is provided. The hotspot testing apparatus comprises a thermal imaging camera configured todetect heat distribution over a top surface of a solar cell, where thetop surface is absent of any metal conductors. Additionally included isa chuck disposed below the thermal imaging camera. The chuck comprises abase portion and a support portion configured to support the solar cellabove the base portion and configured to define a space, between abottom surface of the solar cell and the base portion, that thermallyseparates a portion of the bottom surface of the solar cell from thebase portion. Here, the bottom surface has metal conductors. The chuckfurther comprises a bore through at least the base portion andadditionally comprises a probe disposed below the chuck. This probe isconfigured to make contact with the metal conductors through the boreand to apply a negative bias voltage to the solar cell.

In yet another embodiment, a chuck to support a solar cell in hot spottesting is provided. This embodiment of the chuck comprises a baseportion and a support portion disposed above the base portion. Thesupport portion is configured to support the solar cell above the baseportion and to define a space, between a bottom surface of the solarcell and the base portion, that thermally separates a portion of thebottom surface of the solar cell from the base portion.

In one other embodiment, a method of hot spot testing a solar cell,which has a top surface and a bottom surface, is provided. In thismethod, the solar cell is transported over a chuck. This chuck comprisesa base portion and a support portion disposed above the base portion.The support portion is configured to support the solar cell above thebase portion and configured to define a space, between the bottomsurface of the solar cell and the base portion, that thermally separatesa portion of the bottom surface of the solar cell from the base portion.In this embodiment, the portion of the bottom surface that is thermallyseparated comprises between about 70% and about 90% of the bottomsurface. Here, the bottom surface of the solar cell has metal conductorswhile the top surface is absent of any metal conductors. The chuckfurther comprises a bore through the base portion and the supportportion, a side portion, and a vacuum tunnel having openings at twoends, where one of the openings is located within substantially a sameregion of the bore and another of the openings is located at the sideportion. In this method, a vacuum suction is applied through the vacuumtunnel to hold the solar cell in place, and a negative bias voltage isapplied to the solar cell through the metal conductors. A heatdistribution of the top surface is detected upon application of thenegative bias voltage.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 depicts a hot spot testing apparatus, in accordance with anembodiment of the present invention;

FIG. 2 depicts a thermal image of a top surface of the solar cell duringhot spot testing;

FIG. 3 depicts a diagram of a cross-sectional view of an example of asolar cell;

FIGS. 4A and 4B depict different views of a chuck, in accordance with anembodiment of the present invention, configured to support a solar cellin a hot spot testing apparatus;

FIGS. 5A, 5B, 5C, and 5D depict various views of one or more chucks, inaccordance with an alternate embodiment of the present invention,configured to support a solar cell in a hot spot testing apparatus; and

FIG. 6 depicts a flow diagram of a general overview of a method inaccordance with an embodiment for hot spot testing solar cells.

DETAILED DESCRIPTION

The following description and the drawings illustrate specificembodiments of the invention sufficiently to enable those skilled in theart to practice them. Other embodiments may incorporate structural,logical, electrical, process, and other changes. Examples merely typifypossible variations. Individual components and functions are optionalunless explicitly required, and the sequence of operations may vary.Portions and features of some embodiments may be included in orsubstituted for those of others. Embodiments of the invention set forthin the claims encompass all available equivalents of those claims.Embodiments of the invention may be referred to, individually orcollectively, herein by the term “invention” merely for convenience andwithout intending to limit the scope of this application to any singleinvention or inventive concept if more than one is in fact disclosed.

FIG. 1 depicts a hot spot testing apparatus 100, in accordance with anembodiment of the present invention. The hot spot testing apparatus 100tests an ability of the solar cell 104 to withstand hot spot heating. Inthis example, the hot spot testing apparatus 100 includes a thermalimaging camera 102, a solar cell 104, a chuck 106, and probes 108. Thesolar cell 104 is placed on top of the chuck 106, which is configured tohold or support the solar cell 104. To test the solar cell 104 for hotspots, the probes 108 disposed below the chuck 106 are configured tomake contact with metal conductors located on the bottom of the solarcell 104 and apply a negative bias voltage. As explained in more detailbelow, the chuck 106 may include bores (not shown) from which the probes108 pass through in order to make contact with the metal conductors.

With the application of the negative bias voltage, the solar cell 104becomes, for example, short-circuited and dissipates power in the formof heat. The thermal imaging camera 102, which is disposed above thesolar cell 104, can detect this heat distribution over a surface of thesolar cell 104. For example, FIG. 2 depicts a thermal image of a topsurface of the solar cell 104 during hot spot testing. As depicted, theapplication of the negative bias voltage generates localized heating ofthe solar cell 104 where regions of the solar cell 104 are heated todifferent temperatures that range from, for example, 20° C. to 26° C.From the thermal image detected by the thermal imaging camera 102,depicted in FIG. 1, the ability of the solar cell 104 to withstand hotspot heating can be identified.

FIG. 3 depicts a diagram of a cross-sectional view of an example of asolar cell 104. The solar cell 104 employs a silicon wafer 301 having atop surface 302 configured to face the sun to receive solar radiationand a bottom surface 304 where metal conductors 306 to the solar cell104 are formed. The solar cell 104 includes p-type polysilicon regions308 and n-type polysilicon regions 310 formed in a polysilicon layer onthe bottom surface 304 of the solar cell 104. The bottom surfacepolysilicon layer may be doped to have the p-type polysilicon regions308 and n-type polysilicon regions 310, with each adjacent p-typepolysilicon region 308 and n-type polysilicon region 310 forming a p-njunction. Metal conductors 306 are connected to the p-type polysiliconregions 308 and n-type polysilicon regions 310 to allow externalcircuits and devices to receive electrical power from the solar cell104, or alternatively, to allow external circuits and devices to deliverelectrical power to the solar cell 104 in hot spot testing. Given thatthe polysilicon layer is formed on the bottom surface 304 of the solarcell 104, the top surface 302 is absent of any metal conductors, asdepicted in FIG. 3.

FIGS. 4A and 4B depict different views of a chuck 400, in accordancewith an embodiment of the present invention, configured to support asolar cell 104 in a hot spot testing apparatus, such as the hot spottesting apparatus 100 depicted in FIG. 1. In particular, FIG. 4A depictsa top view of the chuck 400 while FIG. 4B depicts a side view of thechuck 400 in support of a solar cell 104. In this embodiment, the chuck400, as depicted, is rectangular in shape, but it should be appreciatedthat in other embodiments, the chuck 400 may be formed in a variety ofother shapes, such as squares, triangles, ovals, and circles. The chuck400 includes a base portion 404 and support portions 402 that, asdepicted in FIG. 4B, are disposed above the base portion 404. The chuck400 additionally includes bores 406 through the base portion 404 and thesupport portions 402.

The support portions 402 are configured to support the solar cell 104above the base portion 404. As depicted in FIG. 4A, the support portions402 are shaped as rectangles, but may be any suitable shape and/or sizesuch as, for example, squares, ovals, cylinders, and triangles. Itshould be noted that in hot spot testing, heat generated from the solarcell 104 is transferred to the chuck 400. To possibly reduce the amountof heat transferred to the chuck 400, the surface area of contactbetween the bottom surface (such as bottom surface 304 of FIG. 3) of thesolar cell 104 and the chuck 400 can be minimalized by supporting thesolar cell 104 with the support portions 402 rather than the entiresurface of the chuck 400.

Additionally, the support portions 402 define a space 409, as depictedin FIG. 4B, between the bottom surface of the solar cell 104 and thebase portion 404. That is, the elevation of the solar cell 104 above thebase portion 404 of the chuck 400 creates a space 409. This space 409may, in one embodiment, be greater than or equal to about 0.5millimeters. In another embodiment, the space 409 may be greater than orequal to about 1.5 millimeters. As used herein, the term “about” meansthat the specified dimension or parameter may be varied within anacceptable tolerance for a given design or application. In someembodiments, for example, an acceptable tolerance for a parameter is±10%. It should be noted that this space 409 serves to thermallyseparate a portion of the bottom surface of the solar cell 104 from thebase portion 404. As used herein, “thermal separation” refers to atemperature division between two or more areas at differenttemperatures. In effect, the space 409 serves as insulation between thebase portion 404 and the bottom surface of the solar cell 104. The spacemay reduce the amount of heat transferred from the base portion 404 ofthe chuck 400 to the solar cell 104. For example, thermal separation canbe defined in terms of thermal conductivity of a material, liquid, orgas that, as discussed above, thermally separates the base portion 404from the bottom surface of the solar cell 104. In one example, thethermal conductivity of air is about 0.025 W/(m*K).

Still referring to FIGS. 4A and 4B, the bores 406 are holes through, forexample, the base portion 404 and the support portions 402. As discussedabove, the example of the solar cell 104 depicted in FIG. 4B has abottom surface where metal conductors are formed. In hot spot testing,probes apply negative voltage to the solar cell 104 through the metalconductors. The bores 406 allow such probes to pass through in order tomake contact with the metal conductors.

FIGS. 5A and 5B depict various views of chucks 500 and 500′, inaccordance with an alternate embodiment of the present invention,configured to support a solar cell in a hot spot testing apparatus, suchas the hot spot testing apparatus 100 depicted in FIG. 1. As depicted inFIGS. 5A and 5B, the chucks 500 and 500′ are configured to support orhold a solar cell (not shown) in hot spot testing and are separated by achannel 514. FIG. 5A depicts a top view of the chucks 500 and 500′ whileFIG. 5B depicts a side view of one chuck 500. In this alternateembodiment, each chuck 500 or 500′ includes a base portion 508 (asillustrated with a hatched pattern in FIG. 5A) and a support portion 510that is disposed above the base portion 508. Additionally, each chuck500 or 500′ includes bores 504, mounting holes 502, vacuum tunnelopenings 505 and 506, and straight channels 512. The bores 504, asdiscussed above, are configured to allow probes to make contact with themetal conductors formed on the bottom surface of a solar cell. Themounting holes 502 are used to secure the chucks 500 and 500′ to, forexample, a table included in a hot spot testing apparatus. The chucks500 and 500′ may be secured with screws, bolts, or other fasteners.

The support portion 510 is configured to support the solar cell abovethe base portion 508 and to define a space between the bottom surface ofthe solar cell and the base portion 508. In the embodiment depicted inFIG. 5A, the portion of the bottom surface of the solar cell that isthermally separated comprises between about 70% and about 90% of thebottom surface. In other words, about 10% to about 30% of the bottomsurface is supported by the support portion 510. In one embodiment, atleast about 26% of the bottom surface of a 150 mm×150 mm solar cell issupported by the two chucks 500 and 500′ depicted in FIG. 5A. As aresult of the thermal separation created by the space between the bottomsurface of the solar cell and base portion 508, the amount of heattransferred from the solar cell to the chucks 500 and 500′ may bereduced to between about 0.020W/(m*K) and 0.030 W/(m*K).

In addition to supporting the solar cell, the chucks 500 and 500′ alsohold the solar cell in place during hot spot testing. In one example,the solar cell can be held in place with the use of vacuum suction. Thevacuum can be applied through vacuum tunnels to force the bottom surfaceof the solar cell to adhere to a surface of the support portion 510.Each vacuum tunnel has at least two openings 505 and 506. As depicted inFIG. 5B, each chuck 500 or 500′ includes at least one side, and in oneembodiment, one vacuum tunnel opening 505 can be located at the side.The other vacuum tunnel openings 506 may be located on a surface of thesupport portion 510.

FIG. 5C depicts a magnified view of a support portion 510 having avacuum tunnel opening 506 located near a bore 504. In one embodiment,each vacuum tunnel opening 506 located at the surface of the supportportion 510 can be located within substantially the same region of thebore 504. As used herein, the term “substantially” means that thespecified dimension may extend within an acceptable tolerance for agiven application. This dimension may depend on the geometry or shape ofthe vacuum tunnel opening 506 and/or the bore 504, the force of theapplied vacuum, and/or the force applied by probes when in contact withthe solar cell. In one embodiment, a distance 511 or dimension between avacuum tunnel opening 506 and a bore 504 may range from about 1millimeter to about 2 millimeters. For example, the distance 511 may beabout 1.9 millimeters. In the embodiment depicted in FIG. 5C, the vacuumtunnel openings 506 are located substantially within the same region ofthe bores 504 to possibly reduce, for example, the sheer force appliedto a cell solar cell resulting from the vacuum force and an oppositeforce applied by probes when in contact with the bottom surface of thesolar cell. As depicted in FIGS. 5A-5C, each vacuum tunnel opening 505or 506 is circular or crescent in shape, but it should be appreciatedthat in other embodiments, the vacuum tunnel openings 505 or 506 may beformed in a variety of other shapes, such as rectangles and ovals.

The support portions of the chucks 500 and 500′ also include a number ofstraight channels 512, and FIG. 5D depicts a magnified view of thesestraight channels 512. Each solar cell has a corner, and a number ofthese straight channels 512 are configured to contact a portion of thecorner. Given that each channel of the straight channels 512 isseparated from the other channels by a space, the straight channels 512are configured to reduce surface contact of the support portion 510 withthe corner of the solar cell. In one example, the straight channels 512may be located within the vicinity of corners of the solar cell toaccommodate the different sizes of the solar cells, such as 150 mm×150mm, 125.50 mm×125.50 mm, and other sizes. For example, a corner of alarge solar cell is in contact with a larger number of straight channels512 when held in place by a chuck compared to a smaller solar cell.

It should be appreciated that the chucks 500 and 500′ may be comprisedof a variety of different materials. In one embodiment, heat transfermay be further reduced with the use of plastic polymers. Examples ofplastic polymers include polyether ether ketone (PEEK), GAROLITE, MCNYLON, polyoxybenzylmethylenglycolanhydride (BAKELITE), MICROTHERM SUPERG, and other plastic polymers. In one embodiment, the plastic polymerhas a thermal conductivity between about 0.250 W/(m*K) and about 0.288W/(m*K). Examples of such plastic polymers include PEEK and GAROLITE.Additionally, the selection of the plastic polymer for the chucks 500and 500′may be based on the tensile strength of the plastic polymer. Inone embodiment, the plastic polymer may have a tensile strength betweenabout 95 MPa and about 100 MPa. Examples of plastic polymers withtensile strengths in this range include PEEK and MC NYLON.

FIG. 6 depicts a flow diagram of a general overview of a method 600 inaccordance with an embodiment for hot spot testing solar cells. In anexample embodiment, the method 600 may be implemented by the hot spottesting apparatus 100 depicted in FIG. 1. As depicted in FIG. 6, a solarcell is transported over a chuck at 602. In this example, the solar cellhas a top surface and a bottom surface, where the bottom surface hasmetal conductors while the top surface is absent of any metalconductors. The chuck that supports the solar cell has a base portionand a support portion disposed above the base portion, as describedabove.

To hold the solar cell in place, vacuum suction is applied at 604through vacuum tunnels of the chuck. With the solar cell held in place,probes may make contact with the bottom surface of the solar cell andapply, at 606, a negative bias voltage to the solar cell through themetal conductors. With the negative all bias voltage applied, regions ofthe solar cell are heated, and at 608, the heat distribution on the topsurface of the solar cell is detected. After the heat distribution isdetected, vacuum suction is stopped and the solar cell, which is heated,is transferred away from the chuck. The method 600 is then repeated foranother solar cell. The use of the chuck as described above to supportthe solar cell may, for example, reduce the amount of heat transferredfrom the heated solar cell to the chuck. Thus, the chuck may not besignificantly heated during hot spot testing. A subsequent solar cellcan therefore be quickly transported over the chuck without the chucktransferring significant heat from a previous hot spot test. As aresult, the use of the various embodiments of chucks described above inhot spot testing may, for example, facilitate the testing of a largenumber of solar cells for hot spots in a relatively short amount oftime.

In the foregoing detailed description, various features are occasionallygrouped together in a single embodiment for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments of the subjectmatter require more features than are expressly recited in each claim.Rather, as the following claims reflect, the invention may lie in lessthan all features of a single disclosed embodiment. Thus the followingclaims are hereby incorporated into the detailed description, with eachclaim standing on its own as a separate preferred embodiment.

Plural instances may be provided for components, operations orstructures described herein as a single instance. Finally, boundariesbetween various components, operations, and data stores are somewhatarbitrary, and particular operations are illustrated in the context ofspecific illustrative configurations. Other allocations of functionalityare envisioned and may fall within the scope of the invention(s). Ingeneral, structures and functionality presented as separate componentsin the exemplary configurations may be implemented as a combinedstructure or component. Similarly, structures and functionalitypresented as a single component may be implemented as separatecomponents. These and other variations, modifications, additions, andimprovements fall within the scope of the invention(s).

What is claimed is:
 1. A chuck to support a solar cell having a topsurface and a bottom surface in hot spot testing, the chuck comprising:a base portion; a support portion disposed above, and coupled to, thebase portion, the support portion to support the solar cell above thebase portion and to define a cavity between the bottom surface of thesolar cell and the base portion that thermally separates a portion ofthe bottom surface of the solar cell from the base portion; and a borethrough the base portion and the support portion, the bore to allow aprobe to make contact with metal conductors of the bottom surface of thesolar cell through the bore.
 2. The chuck of claim 1, wherein the chuckis heated during the hot spot testing, and wherein the cavity reduces anamount of heat transferred from the base portion of the chuck to thesolar cell.
 3. The chuck of claim 2, wherein the amount of heattransferred is reduced to between about 0.020 W/(m*K) and 0.030 W/(m*K).4. The chuck of claim 1, wherein a portion of the support portioncomprises straight channels, and wherein a number of the straightchannels is to contact a corner of the solar cell and to reduce surfacecontact of the support portion with the corner.
 5. The chuck of claim 1,wherein the chuck comprises a vacuum tunnel having openings at two ends,one of the openings being located within substantially a same region ofthe bore and another of the openings being located at a side of thechuck.
 6. The chuck of claim 1, wherein the chuck is comprised of aplastic polymer.
 7. The chuck of claim 6, wherein the plastic polymerhas a thermal conductivity between about 0.250 W/(m*k) and about 0.288W/(m*k).
 8. The chuck of claim 6, wherein the plastic polymer has atensile strength between about 95 MPa and about 100 MPa.
 9. A hot spottesting apparatus, comprising: a thermal imaging camera to detect heatdistribution over a top surface of a solar cell; a chuck disposed belowthe thermal imaging camera, the chuck comprising a base portion and asupport portion coupled to the base portion, the support portion tosupport the solar cell above the base portion and to define a cavitybetween a bottom surface of the solar cell and the base portion thatthermally separates a portion of the bottom surface of the solar cellfrom the base portion, and the chuck further having a bore through atleast the base portion; and a probe disposed below the chuck, the probeto make contact with metal conductors of the bottom surface of the solarcell through the bore.
 10. The hot spot testing apparatus of claim 9,further comprising an additional chuck disposed below the thermalimaging camera, the additional chuck comprising an additional baseportion and an additional support portion to support the solar cellabove the additional base portion and to define an additional cavity,between the bottom surface of the solar cell and the additional baseportion, that thermally separates an additional portion of the bottomsurface of the solar cell from the additional base portion.
 11. The hotspot testing apparatus of claim 10, wherein the chuck is separated fromthe additional chuck by a channel.
 12. The hot spot testing apparatus ofclaim 10, wherein at least about 26% of the bottom surface of the solarcell is supported by the support portion and the additional supportportion.
 13. A chuck to support a solar cell in hot spot testing, thechuck comprising: a base portion; and a support portion disposed above,and coupled to, the base portion, the support portion to support thesolar cell above the base portion and to define a cavity between abottom surface of the solar cell and the base portion that thermallyseparates a portion of the bottom surface of the solar cell from thebase portion, wherein a portion of the support portion comprisesstraight channels, and wherein a number of the straight channels is tocontact a corner of the solar cell, and wherein the chuck has a borethrough at least the base portion, and wherein the bore is to allow aprobe to make contact with the bottom surface of the solar cell throughthe bore.
 14. The chuck of claim 13, wherein the support portioncomprises a surface to contact a different portion of the bottom surfaceof the solar cell, wherein the chuck further comprises a side portion,and wherein the chuck comprises a vacuum tunnel having openings at twoends, one of the openings being located within substantially a sameregion of the bore, another of the openings being located at the sideportion.
 15. The chuck of claim 13, wherein the chuck is comprised of aplastic polymer.
 16. The chuck of claim 15, wherein the plastic polymerhas a thermal conductivity between about 0.250 W/(m*K) and about 0.288W/(m*K).
 17. The chuck of claim 15, wherein the plastic polymer has atensile strength between about 95 MPa and about 100 MPa.
 18. The chuckof claim 15, wherein the plastic polymer has a thermal conductivitybetween about 0.250 W/(m*K) and about 0.288 W/(m*K), and wherein theplastic polymer has a tensile strength between about 95 MPa and about100 MPa.
 19. The chuck of claim 13, wherein the portion of the bottomsurface of the solar cell that is thermally separated comprises betweenabout 70% to about 90% of the bottom surface.
 20. The chuck of claim 13,wherein the chuck is comprised of a plastic polymer, and wherein theportion of the bottom surface of the solar cell that is thermallyseparated comprises between about 70% to about 90% of the bottomsurface.